mktree: validate entry type in input

Previously mktree would accept tree entries which had a mismatch between
the declared type and the actual type of object.  Check the actual type of
the object when it is available locally.

Signed-off-by: Josh Micich <josh.micich@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-mktree.c

@@ -71,7 +71,8 @@ static void mktree_line(char *buf, size_t len, int line_termination, int allow_m
 {
 	char *ptr, *ntr;
 	unsigned mode;
-	enum object_type type;
+	enum object_type mode_type; /* object type derived from mode */
+	enum object_type obj_type; /* object type derived from sha */
 	char *path;
 	unsigned char sha1[20];
 
@@ -94,17 +95,8 @@ static void mktree_line(char *buf, size_t len, int line_termination, int allow_m
 	if (S_ISGITLINK(mode))
 		allow_missing = 1;
 
-	if (!allow_missing)
-		type = sha1_object_info(sha1, NULL);
-	else
-		type = object_type(mode);
-
-	if (type < 0)
-		die("object %s unavailable", sha1_to_hex(sha1));
 
 	*ntr++ = 0; /* now at the beginning of SHA1 */
-	if (type != type_from_string(ptr))
-		die("object type %s mismatch (%s)", ptr, typename(type));
 
 	path = ntr + 41;  /* at the beginning of name */
 	if (line_termination && path[0] == '"') {
@@ -113,6 +105,37 @@ static void mktree_line(char *buf, size_t len, int line_termination, int allow_m
 			die("invalid quoting");
 		path = strbuf_detach(&p_uq, NULL);
 	}
+
+	/*
+	 * Object type is redundantly derivable three ways.
+	 * These should all agree.
+	 */
+	mode_type = object_type(mode);
+	if (mode_type != type_from_string(ptr)) {
+		die("entry '%s' object type (%s) doesn't match mode type (%s)",
+			path, ptr, typename(mode_type));
+	}
+
+	/* Check the type of object identified by sha1 */
+	obj_type = sha1_object_info(sha1, NULL);
+	if (obj_type < 0) {
+		if (allow_missing) {
+			; /* no problem - missing objects are presumed to be of the right type */
+		} else {
+			die("entry '%s' object %s is unavailable", path, sha1_to_hex(sha1));
+		}
+	} else {
+		if (obj_type != mode_type) {
+			/*
+			 * The object exists but is of the wrong type.
+			 * This is a problem regardless of allow_missing
+			 * because the new tree entry will never be correct.
+			 */
+			die("entry '%s' object %s is a %s but specified type was (%s)",
+				path, sha1_to_hex(sha1), typename(obj_type), typename(mode_type));
+		}
+	}
+
 	append_to_tree(mode, sha1, path);
 }